Rudbeckia auriculata

Rudbeckia auriculata

Rudbeckia auriculata (The eared coneflower) is a tall Rudbeckia native to acid bogs in the southeast USA.

Etymology

The specific epithet ‘auriculata’ (meaning with ears), refers to the lobed clasping attachment of the upper leaves to the stem . The species was described by Robert Edward Perdue.

Taxonomy

Previously R. auriculata has been treated as a variety of R. fulgida . However, in 1957 it was noted that it varied considerably from the ‘fulgidas'’, such that treating it as a variety would conflict with species concepts within the Rudbeckia genus , consequently in 1975 'R. fulgida var. auriculata' gained species status becoming R. auriculata. This revision revealed the species' close relationship to other coneflowers including R. nitida and R. mohrii, species which along with R. auriculata are now placed in the subgenus macrocline . R. auriculata is commonly misidentified as R. scabrifolia and sequencing has now revealed they are closely related. Evidence of their close relationship comes from Internal transcribed spacer sequence (ITS) data as well as the generation of spontaneous garden hybrids between these Rudbeckias .

Morphology

R. auriculata is conspicuous in the wild due to its extreme height (occasionally over 3m) making the species easy to identify as long as the morphological differences between it and the closely related and equally tall Rudbeckia laciniata are understood (e.g. ‘laciniatas’ dissected leaves) . The eared coneflower (R. auriculata) is a long-lived perennial. The lower leaf blades are up to 65 cm long and attached to the stem by a petiole, they are arranged alternately along the stem. Progressing up the stem the leaves decrease in size and the petioles are lost, the attachment of the leaves to the stem is now auriculate . The flowers are arranged in a panicle containing a dozen bright yellow ray flowers. If fertilized, purple-brown achenes are produced which are approximately 4-5mm long . R. auriculata is classified within the section macroline. In contrast with the more typical macroline, R. auriculata has smaller seeds as well as having the species defining feature ‘auriculate leaves’.

Growth and Reproduction

Studies show R. auriculata is pollinated by the mining bee Andrena aliciae where plants exist in large numbers. In contrast, when populations are small the most numerous pollinators are bees in the family Halictidae. A species of pollen mimic fungus Fusarium semitectum takes advantage of the plant pollinator relationship. The fungus spores are similar in morphology to Rudbeckia pollen and are transported between flowers by Andrena aliciae. The fungus sporulates on the disk flowers in order to increase its chances of dispersal as the disk flowers are in closest contact with pollinating insects. Artificial pollination experiments reveal that few fertile seeds are produced from self-pollination meaning the plant is xenogamous (requiring cross pollination). If pollinated the achenes mature and once seed is ripe the seedheads slowly break apart releasing seeds in close proximity to the plant . Once dispersed, seeds require cold stratification in order to germinate once temperatures rise and photoperiod lengthens. To germinate, these seeds need a suitable seedbed of bare soil, such as would be produced after herbaceous plants and shrubs are cleared by fire or when buried soils are uplifted by stream scouring. Because these events are infrequent and fires are often suppressed by humans, seedlings are rarely recorded in the wild . Despite its ineffective seed dispersal, this species can spread through clonal reproduction. Resultantly, often the entire population consists of a single genet.

Distribution and habitat

Rudbeckia auriculata is endemic to the USA especially the southeast. Most recorded populations are found in Alabama with one other population occuring in Georgia. Previously this species was found in Florida but this population is now presumed to be extinct. The distribution and population of this species is reducing, with the majority of sites producing fewer than 50 flowering stems per year . R. auriculata along with the closely related R. scabrifolia and R. morhii occupy habitats such as peat bogs and can be found in disturbed areas such as alongside roads and within grazed fields. Healthy beaver populations support R. auricuata by engineering rivers to slow waterflow and create bog habitats. R. auriuclata is found in similar habitats to R. scabrifolia and of Sarracenia .

Conservation

Several factors limit the population size of R. auriculata, these include poor seed set due to fungal pathogens, low dispersal capacity , and low rates of germination. As a result of several population/distribution surveys this species has been added to the Endangered Species Act .

Cultivation

This species is little known in cultivation as it is difficult to grow within a typical mixed or herbaceous border unless provided with boggy soil. Eared coneflower is occasionally available from specialist nurseries but is typically only used in conservation/prairie restoration as well as within botanic gardens . One major drawback is R. auriculatas propensity to lodge, this is most severe when grown in rich soils that differ from the low nutrient peaty soils the species is adapted to .